It has long been recognized that the hardness and coefficient of restitution of the impact face of a golf club will affect the force imparted to the ball when a club is swung with a given speed. Materials which will provide an appropriate range of forces often differ from the material with which the golf head is constructed, so it has been proposed to provide golf clubs with inserts of particular materials chosen for their hardness and rebound coefficients (which will hereinafter be collectively referred to as “impact factors”). U.S. Pat. No. 3,937,474 discloses a golf club with a polyurethane insert on the striking face that provides an advantageous impact factor to balls hit with the club.
It has also been proposed to make these inserts detachable so that the impact face of a club may be altered to provide an insert which is chosen based on the condition of the course. For example, when the greens have short grass and are relatively hard, i.e. “fast”, an insert with a relatively low impact factor is chosen, but when the grass is longer, or damp, so that the green is “slow”, an insert with a high impact factor is chosen. This allows a golfer to use substantially the same stroke with fast and slow greens and to impart forces on the golf ball which are consistent with these conditions. See, for example, U.S. Pat. No. 5,921,871.
Rather than requiring an insert to be changed in order to alter the force induced on a ball using a relatively consistent stroke, it has been proposed to provide a multiple-faced head for a golf putter in which the different faces have different ball-impacting characteristics. U.S. Pat. No. 6,695,708 discloses such an adjustable putter. The head is polygonal in shape and is affixed to the club shaft so that all of the faces lie in the vertical plane when the club is in use. The head has a polygonal socket on its upper surface which mates with a male polygonal member disposed at one end of the hosel so that the hosel may be inserted into the head into a position which supports one of the faces in a ball-impacting position. The head is unusual in shape, in no way resembling a conventional golf putter, and the weighting created by this unusual shape is unconventional and may well be confusing to the golfer.